Help with building your Speeduino, installing it, getting it to run etc.
By kettlekev
#47932
I am trying to work out how Speeduino calculates its fuel load in CC's (volume) and what that number is and if I can see it anywhere?
required fuel.PNG
required fuel.PNG (174.43 KiB) Viewed 4810 times
From the calculator that then decides the injector opening time, you dont get a volume figure.

I am trying to run the smallest injector possible to make the slow running more stable and knowing the CC's injected will help my maths.

I've found a few sites that seem to be able to give the fuel load but they all differ a bit in the answer.
https://mathtab.com/app_id=4033
User avatar
By PSIG
#47937
kettlekev wrote: Sun Jan 31, 2021 10:07 am I am trying to work out how Speeduino calculates its fuel load in CC's (volume) and what that number is and if I can see it anywhere?
Flow volume is based on what you enter in the calculator for volume versus time (300cc/min). Flow volume per-millisecond is simple math, and provides flow per-millisecond for your pulsewidth. In your case it injects (that injector, fuel and and fuel pressure) at 0.005 cc/ms.

The Req_fuel display shows the ms calculated at 100% VE for the engine, in your case, 6.6ms * 0.005cc = 0.033 cc/cycle. To see what factors are involved in fuel calculations (and a good verification that factors are correct or expected ;)) is to load the Calculations.dash from your firmware files into TunerStudio, and watch the calculations real-time. 8-) Calculations.dash is specific to each firmware version.
kettlekev wrote: Sun Jan 31, 2021 10:07 amI am trying to run the smallest injector possible to make the slow running more stable and knowing the CC's injected will help my maths.
There are many factors affecting flow rate, so if you have a goal of low-load fuel control, these factors may be altered in your favor. Injector rated flow (cc/min @ rating psi with specific fuel properties) is just one factor. For example, the fuel pressure regulator is often MAP-referenced (MRFPR) in order to reduce low-MAP (low-load) fuel pressure, increasing the PW necessary for fuel delivery and the time available to control it, increasing accuracy. It has other benefits, such as creating a more linear fueling curve when the differential pressure across the injector is held more consistent. In more extreme cases (e.g., huge injectors), a rising-rate FPR can extend the differential favorably at low loads, with limits. There are other methods and options.
By kettlekev
#48015
PSIG

Brilliant. Thanks. I will absorb that. I've built a calculator that once I enter load, injector size etc. I can work out start and end injection points across the rev range and tune the injector size. I know Speeduino allows you to enter end inject points and it works out start points for you but I just wanted to get my head around it.

I am looking at direct injecting into the underside of the crankcase to get fuel up under the piston (cooling etc.), so just trying to get a picture of what happens when.

Thanks...
By kettlekev
#48022
PSIG...having read a few times I get....
Flow volume is based on what you enter in the calculator for volume versus time (300cc/min). Flow volume per-millisecond is simple math, and provides flow per-millisecond for your pulsewidth. In your case it injects (that injector, fuel and and fuel pressure) at 0.005 cc/ms.
.

I see that 300cc injector at 6.6ms = 0.005cc, but what defines the 0.005cc, how do I know my engine needs 0.005cc to generate the HP I want?

I know there is the required fuel calculator that asks for capacity and AFR etc. but what is the maths behind that?

Will the calculations dash you referenced give me that?

The website I mentioned it my first post seemed to make sense, I will try to cross reference the two if the dash is what you think will provide the answer to my question?

Cheers :D
By LPG2CV
#48025
I think generally speaking, injectors are listed by HP. The volume of fuel delivery will also be listed.

The bottom line is, if you want to produce 100 HP, then you have to provide the fuel need for that 100 HP.

The mistake I made when I ventured into buying injectors (used £10 for 4 including fuel rail :) ) for my classic car conversion, was to try to match my engine capacity to other more modern makes and models. My car is 2 cylinder and 602cc, so I looked for a 4 cylinder 1200cc engine.

The mistake is that my engine with 2 cylinders produces about 30 HP, where as the engine I matched to, produced 85 HP. About half as big again oversize.

So, research injectors available for the HP of your engine, look up the flow rate, and you should be able to do your math from there.

Don't forget the 85% duty limit is there to allow for AE and WUE etc. :)
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By PSIG
#48026
kettlekev wrote: Tue Feb 02, 2021 11:14 pm I see that 300cc injector at 6.6ms = 0.005cc, but what defines the 0.005cc, how do I know my engine needs 0.005cc to generate the HP I want?
You don't, unless you know the specific fuel consumption of your specific engine setup with specific fuel, and 101 other factors. Specifically. :lol: Seriously, unless you know how efficient your engine (and all supporting parts) are, you can only judge an estimate, as SFCs vary wildly. You can imagine that a '65 Beetle and a '21 BMW will have very different ability to convert fuel to power, and that less-efficient designs will need more fuel to make the same power. Different fuels and blends extend that difference as well.

That said, I'll link to Eric Fahlgren's Not2Fast site and its Turbo Calculator page for some mental exercise and relationship building. While still relatively rudimentary, it provides some very interesting information on efficiencies and how changes alter other numbers, including your question of how much fuel for how much power. So, my suggestion is to model an engine in there that is well known to you. It doesn't have to be turbo. ;) If not boosted, zero the boost and intercooler pressure drop for a normally-aspirated engine.

Model the engine using the power, rpm, and other numbers you know for that engine. See how efficient it is when you change the numbers to make it fit. Try altering the Volumetric Efficiency and the SFC to initially see how those each effect results in power and fuel injector flow. The instructions and other stuff on his site are scratching the surface, but in a way that shows how one parameter or concept can lead to the next.
kettlekev wrote: Tue Feb 02, 2021 11:14 pmI know there is the required fuel calculator that asks for capacity and AFR etc. but what is the maths behind that?
They are standardized calculations, using your entered info to estimate the values similarly to what you see in Eric's calculator. Eric tells how that info is used, or refers to it.
kettlekev wrote: Tue Feb 02, 2021 11:14 pmWill the calculations dash you referenced give me that?
No, but it will lead you to them.
By kettlekev
#48042
Thanks guys. All good stuff, I will play with that.

So all that said it seems the best way is trial and error. Start in the ballpark and watch the dyno. Luckily it is re programmable!!

I should be running up the ignition side of the project this weekend, so all good so far.

Injector positioning is a challenge on a 3 cylinder, 2 stroke with oil injection but I have a plan so lets see......

Thanks again
By kettlekev
#48814
Starting to look at the injectors properly now that ignition is running.

Because for my 3 cylinder 2 stroke, I have to tell speedy its a 6 cylinder, wasted spark to get it to fire 1,2,3 (see below).....
fuel1.PNG
fuel1.PNG (149.54 KiB) Viewed 4355 times
When I run the required fuel maths to control the VE table, I assume it is using the 6 cylinder Required Fuel number of 5.6ms.

This will then be twice what I need in the VE?

I cant change the required fuel cylinders to 3 because then I think it mess's up my wasted spark 3 cylinder setting and the firing will be wrong?

How do I set the right fuel number for the VE?

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